The present invention is directed generally to the electrical stimulation of both bone fractures and soft tissue to promote and expedite the healing thereof, and more particularly to a small thin invasive electrical stimulation device which can be easily implanted and which is operative to both monitor the healing process and to adjust the electrical stimulation in response thereto.
The general acceleration of bone fracture healing from electrical stimulation has been appreciated in the past, for example, in the analysis of Wolfian laws of soft tissue collagenous structures to fields. It is known that some specific functional link serves to transduce express electrical energies into a mechanical response, namely bone deposition, formation and cell differentiation. Cells respond and orientate to direct current field patterns under stimulation of cathode placement.
Certain minimum current is required to facilitate an initiating response to stimulus and to change the healing progression of bone and soft tissue. Optimal response amperage is approximately 20 microamps. Reduced amperage minimizes necrosis and increased amperage tends to maximize healing potential within finite variables.
Studies have shown electrical stimulation to effect nuclear and cytoplasmic RNA, pH of extra cellular environment which have been recorded to achieve optimal environments for manipulation of the osteoblastic response, increased DNA content, and organelle components of the cytoplasm, all of which reflect an advantageous facilitative response to healing.
The extracellular products of such cell types responding to electrical stimulation have been noted to respond in an organizational way to such fields, and might relate to extracellular-intracellular feedback mechanisms of control believed to be related to current density of stimulation and time sequence of need in healing fractures, which this invention addresses.
Osteogenesis has generally been performed by an only semiinvasive method. An example is the direct current bone growth stimulator marketed by Zimmer of Warsaw, Ind. 46580 and licensed under U.S. Pat. No. 3,842,841. In this system, several cathode needles are inserted through the skin into a bone fracture. An anode pad is externally situated adjacent the fracture and an external power source electrically connects the anode and cathode leads. Disadvantages of such known systems include the need for the patient to maintain the external device environment and the hazards of injury or accidental interruption in the patient's daily life routine. Whereas an implantable needle-like bone growth stimulator is disclosed in U.S. Pat. No. 4,333,469, no such device has previously been known which is sheet-like in construction and which is capable of progressively monitoring the healing response of a fracture to electrical stimulation and manipulating the current output of the apparatus for maximizing the potential healing response of bone and soft tissue repair.
Accordingly, a primary object of the invention is to provide an improved apparatus and method for the invasive electrical stimulation of bone fractures.
Another object is to provide an electrical stimulation device for bone fractures and soft tissue which is totally encapsulated and implantable so as to be much less cumbersome than externally supported devices and adaptable for healing more types of injuries.
Another object is to provide an apparatus and method of invasive electrical stimulation which include a novel cathode and anode designed for increased operative surface area.
Another object is to provide such an apparatus and method wherein the current density and timing of the output of the implanted power source can be externally monitored and adjusted.
Another object is to provide such an apparatus and method wherein the healing response of a fracture is monitorable at a plurality of positions and over a period of time.
Finally, an object is to provide a wholly invasive electrical stimulation device which is simple and rugged in construction, readily implantable, and efficient in operation.